Conventional slitting devices used for slitting thin media, such as photographic paper and film, employ some sort of biasing member to control the contact force between cooperating blades or knife members. Typically such media is mass produced in large width master coils and then is cut to narrow width coils from the master coil using such slitting knives. Skilled artisans will appreciate that contact force is the force that one blade member exerts upon the other during a cutting operation.
Some success has been achieved in the art with a variety of biasing members, typically springs, presently used for biasing slitter blade members in an attempt to control the contact force between contacting blades. As shown in prior art FIGS. 1 and 2, the contact force between existing displaceable and stationary slitter knives or blade members 10, 12 is typically created by using a spring system 14 behind the displaceable blade member or knife 10. Various types of springs are currently in use, including coil 16 (illustrated in FIG. 3A), Belleville.TM. 18 (illustrated in FIG. 4A), and garter 20 (illustrated in FIG. 5A). In each of these prior art devices, knives or blades 10, 12, are attached to a knife or blade carrier 22 via some sort of attachment, such as a retainer ring 24 (FIGS. 4A, 5A,), or screws 26 (FIGS. 1-3A). Despite the progress accomplished with the above biasing members, a major shortcoming associated with each of these various biasing springs is that they create uneven spring forces around the circumference of the knife or blade member, as depicted in FIGS. 3B, 4B, and 5B. Experienced artisans will appreciate that these variations in spring force adversely affect the wear of the slitter knives as well as the quality of the slit edge.
Therefore, there persists a need in the art for a slitter element useable in an apparatus for slitting thin media, such as photographic paper and film, that provides uniform media slitting resulting from a uniform contact force between cooperating engaging blade members of the slitting device.